1. Field of the Invention
The present invention relates to glass fiber strand treatment and particularly relates to treating glass fibers during or after forming with an aqueous sizing which prepares the glass fibers for bonding to polyolefins in the reinforcement of polyolefin materials and further has long shelf life and can be used from forming packages formed immediately into mat.
2. Description of the Prior Art
It is known that glass fibers in the form of continuous strands, chopped strands or mats can be used successfully to reinforce polyolefins. And it is known that without effective coupling between the glass and the polyolefin, the adhesion between the two will be weak and separation will occur under shear or tensile stresses. It is further known that the affinity of glass for water aggravates bond weakness when glass is inadequately bonded to polyolefins.
A workable method has been disclosed which permits bonding glass to "lower" polyolefins which are essentially crystalline plastics formed from monomers having three or more carbon atoms. As disclosed in U.S. Pat. No. 3,013,915 at column 2, lines 38-46, glass bonding to polyolefins may be improved by "cleaning the glass surface, applying a coupling agent to it, treating with a chemical agent which is a source of dehydrogenating or oxidizing radicals, contacting the polyolefin with the glass, and fusing it by heating the polyolefin above its melting point to complete the interbonding." At column 4, lines 16-19, the disclosure reveals a preference for radical sources having low decomposition points below 180.degree. F. and at column 4, lines 69-71, indicates that exposure to heat must be avoided.
U.S. Pat. No. 3,849,148 proposes the method of sizing fiber glass strands with an aqueous sizing containing a coupling agent, a heat stable organic peroxide, a non-ionic surfactant and a lubricant. This process was successful in giving some storage capability to the sized strands but did not result in long storage life and further remains susceptible to degradation by high storage temperatures.
U.S. Pat. No. 3,882,068 discloses the sizing composition for glass fibers in several plastic resin systems wherein the size comprises a coupling agent and a polyolefin emulsion.
U.S. Pat. No. 3,437,550 discloses a method of increasing the bonding of glass fibers to polyolefins by treating the fiber with a crystalline polypropylene matrix polymer. The preferred modifiers disclosed are maleic anhydride and acrylic acid.
U.S. Pat. No. 3,883,333 discloses a method and apparatus for forming a continuous glass fiber mat or sized fibers that are suitable for bonding with polyolefins. The process and apparatus disclosed allows lay down of the fibers to form a mat immediately after formation of sized strands.
While the above processes and compositions were useful, there remains a need in the art for a sizing to promote the binding of polyolefins to continuous glass fiber strands with increased adhesion. Further, there remains a need for a sizing for glass fiber strands which will allow the formation of the sized fiber into forming packages or mat that may be stored indefinitely prior to use. Effective sizings containing peroxides have limited shelf-life since they are very sensitive to elevated temperature variations during drying of the fibers and high temperatures during storage which can cause premature degradation of the peroxides thus reducing the effectiveness of the sizing in binding the glass fiber strands to the polypropylene matrix. A problem in forming the fiber mat with continuous lay down after strand formation is that the sizing materials readily cross-link and form deposits on the sizing applicator equipment. These deposits cause delays in production and defects in the mat that is being formed. Therefore there is a continuing need for an improved sizing for continuous lay down mat formation.